Not Applicable.
The invention relates generally to detecting the presence, location and type of coating applied to various transparent mediums, or materials deposited directly to the surface or left on the transparent mediums during the manufacturing process (such as glass or plastic), that may be on a single sheet and/or multiple spaced sheets.
In the coating and glass industry, for example, there are numerous applications where residual coatings from the manufacturing process or spectral reflective coatings are applied to a transparent surface. For example, flat glass is commonly produced by a float process. The float process involves delivering a flow of molten glass at a controlled rate onto a relatively wide bath of molten metal, usually molten tin. The glass, which is buoyant on the molten metal bath, is advanced along the surface of the bath to form a uniform thickness layer which extends laterally across the surface of the bath. As the glass is continuously advanced along the bath, it is sufficiently cooled to permit it to be taken unharmed out of the bath by mechanical means. In the float process, traces of metal or of metallic oxides form on the bottom surface of the glass ribbon as it is removed from the molten metal bath. These oxides are substantially invisible to the naked eye and do not present any deleterious effects to the end use of the glass. However, it has been found that the bottom of the surface of the glass ribbon with the metal oxides has better planimetry than the top surface of the glass ribbon.
In the manufacture of laminated glass products, it is desirable to have the better planimetry on the outer surface. Also, in the process of coating glass with other materials, such as for Low-E windows, the surface containing the metallic oxides also needs to be known for the best performance. Consequently it is desirable to have a process and apparatus for continuously inspecting glass sheets for the surface containing the metallic oxides for identifying the better quality surface of the glass sheets.
U.S. Pat. No. 4,323,785 discloses one method for detecting the presence and locations of transparent metallic oxides on glass sheets. This process uses ultraviolet lamps to cause the metallic oxide to fluorescence and the resulting glow is detected with sensors. This process requires large lamps, which generally must be mounted within an extremely close distance of the material under test. Also, the process uses ultraviolet light which has human safety considerations.
In the coating industry, there also are numerous applications where spectral reflective coatings are applied to a transparent surface. Some of these applications include flat glass, windows, LCD screens, solar cell panels, thermal efficient films, as well as many other plastic and glass applications. During the processing of these flat materials, it is often desirable to have a apparatus that is able to detect the presence and location of the xe2x80x9cinvisiblexe2x80x9d coatings. The coatings may be located on one or both surfaces of a single piece of transparent material, or on one or more surfaces of multiple pieces of transparent material built into an assembly, separated by a known transparent media such as a gas.
It is desirable to have surface coating detection apparatus that can be implemented in a production process that will determine incorrect orientations of surfaces having transparent coatings prior to or during the production process. Many of these industries may not allow the medium to be contacted during the process to prevent contamination of or damage to the coating.
One method of detecting the presence and location of xe2x80x9cinvisiblexe2x80x9d, electrically conductive coatings such as Low-E coatings is described in U.S. Pat. No. 5,132,631. A capacitor is formed between a probe placed against one surface of the glass and the coating. The value of the capacitor is determined by the presence or absence of an electrically conductive coating on the glass and by the location of any coating relative to the probe. This apparatus must contact the medium or be extremely near to the glass under test. The apparatus is limited in its effectiveness by the trade-off of capacitance change versus distance between multiple mediums in parallel. Thus the operator is required to know the glass thickness and air space of the window they are testing. Also the apparatus can not detect the presence of trace metallic oxides left over from the float glass process, determine the type of coating that is present nor detect any reflective characteristics of the coating.
U.S. Pat. No. 5,966,214 discloses a apparatus for measuring the thickness of a sheet of transparent material (such as a sheet of glass), and also for measuring the thickness and spacing of a composite formed from multiple-spaced sheets of glass. A laser beam is directed at an angle to the glass surfaces. The apparatus includes a gauge on which reflections of the laser beam impinge. The spacing between the reflections indicate the thickness of the sheets of glass and the sheet spacings. The apparatus is not designed for indicating the presence of reflective coatings on surfaces of the transparent material. The apparatus also requires that the laser beam be seen by the human eye, and is not designed for an automated production environment. Further, the apparatus was designed to be placed in contact with a surface of the transparent material.
Frequently it is necessary to identify if a transparent coating has been applied to a surface of a transparent medium that is considered a completed product. This completed product may be installed in a final field location. For example, some public utilities provide energy subsidies to homeowners that install specific types of energy efficient windows. It may be necessary to identify if a coating exists within the window assembly, as well as identify the type of coatings on the windows after they are installed in a house. This would allow the public utility to identify the type of coating to verify that the homeowner qualifies for potential energy subsidies.
Apparatus has recently been introduced which attempts to determine the category of a transparent surface coating for Low-E windows. The product classifies the windows as either low solar gain or high solar gain. A high solar gain window is often undesirable in homes located in warm climates. The apparatus consists of a single frequency (or wavelength) light beam that reflects off the coated surface under test. The amplitude of the reflection is measured and the apparatus attempts to determine if the coating is a low or high solar gain Low-E product, or if the glass is clear of a Low-E coating. The apparatus assumes that the surface under test has the same qualities as the surface of a sample used to calibrate the apparatus. Environmental concerns such as dirt on the media or environmental temperature can affect the amount of reflected light sensed by the apparatus. Also, at a fixed light frequency, two or more types of coatings may appear the same. A single point cannot accurately identify multiple coatings that reflect the same amount of relative light energy at a given point in the light frequency spectrum. Finally, this product can not identify the surface location of the spectral reflective coating.
The invention is directed to a method and apparatus for detecting one or more of the presence, location and type of transparent surface coatings present on one or more surfaces of a transparent medium, such as a sheet of glass, or a sheet of plastic, or a composite formed from multiple spaced sheets of glass or plastic. The apparatus may or may not be in contact with the medium under test. The medium may be stationary or moving on a production line.
Depending upon the measurement being made, the apparatus may use one or more light sources. The light sources and sensing apparatus are in fixed positions relative to the medium being tested. A portion of a light beam is reflected from each surface of the material on to the light sensors. The sensors measure the reflections and supply this information to a programmed microcontroller, microprocessor or computer. The reflected signal from the medium under test provides the necessary information to determine the presence, location and/or type of coating. Depending on the desired information, the algorithm may use any combination of the following reflection data:
1. slope relationship of multiple frequency light sources;
2. the absolute value of the reflected signals due to different surfaces of the medium under test;
3. the ratio of reflected energy from each surface of the medium under test; and/or
4. the absolute power amounts of multiple surface reflections that have combined together on a linear type sensing array.
Generally the invention may be designed to operate in at least two configurations: production (factory) or field. The factory often requires apparatus that will not contact the medium under test to ensure that the integrity of the medium is not adversely affected. Field or work-site locations where the medium is being or has been installed in a final location, more often than not allows the medium to be contacted. At this point, the coating is usually sealed between multiple layers of the transparent medium.